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Chapter 5: Manual Operators and Actuators: Section 5.9.9 - Quick Exhaust Valves
By Philip L. Skousen
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From Valve Handbook 2nd Edition
5.9.9 Quick Exhaust Valves Quick exhaust valves are pressure-sensitive venting devices that are used with double-acting actuators in on off applications where positioners are not required. When triggered, quick exhaust valves almost instantaneously vent one side of the double-acting actuator to atmosphere, allowing the valve to move to the full-closed or full-open position. Quick exhaust valves are installed between the air supply and the actuator. As long as a normal air supply is provided to the actuator, normal operation continues. However, when the air supply fails or is interrupted, the quick exhaust valve reacts to the significant differential pressure. An internal diaphragm diverts the exhaust flow coming from the actuator through an enlarged orifice, allowing the internal pressure of the actuator to vent much more quickly. A needle valve must be installed parallel to the quick exhaust valve so that the trip point of the quick exhaust valve can be adjusted, allowing it to react only to large signal demands. Quick exhaust valves are especially helpful with on off applications, where exceptional stroking speeds are required in both directions (see Figs. 5.58 and 5.59). Another common application for quick exhaust valves is when a double-acting actuator with a positioner must provide a fast stroke in one direction (as shown in Figs. 5.60 and 5.61).
© 2009 McGraw-Hill Companies, Inc. (The)
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Air valves allow metered fluid flow in one or both directions. They are used in pneumatic circuits to regulate the rate of activation or exhaust of cylinders and other pneumatic devices.
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Ball valves provide tight shut-off and characterizable control. They have high rangeability due to the design of the regulating element, without the complications of side loads typical of butterfly or globe valves.
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Butterfly valves control flow through a circular disc or vane by turning the valve's pivot axis at right angles to the direction of flow in the pipe. They are normally used as throttling valves to control flow.
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Check valves are self-activating safety valves that permit gases and liquids to flow in only one direction, preventing process flow from reversing. They are classified as one-way directional valves.
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Control valves or proportional valves are power-operated devices used to modify fluid flow or pressure rate in a process system.
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